(car '(0))
;0
(cdr '(0))
;()
(car '((1 2 3) (4 5 6)))
;(1 2 3)
(cdr '(1 2 3 . 4))
;(2 3 . 4)
(cdr (cons 3 (cons 2 (cons 1 '()))))
;(2 1)
